SOP: Cleaning Reusable Anodized-Aluminum Rocket Motor Hardware

For example CTI Pro98 casings, forward/rear closures, and retaining rings.

Purpose

Restore hardware without harming anodized aluminum or seals. Remove corrosive combustion residue promptly after flight [1].

Scope

Applies to CTI Pro98-class hardware and similar anodized 6061-T6 aluminum systems.

Safety

• Wear nitrile gloves, eye protection, and closed-toe shoes.
• Work in a ventilated area, away from ignition sources.
• Only handle hardware after it has cooled completely [1].
• Follow TRA/NAR safety codes.

Approved Cleaners and Compatibility

• Primary cleaner: warm water and mild dish detergent [2].
• Final wipe (optional): isopropyl alcohol (IPA, 90–99%), safe for anodized aluminum.
• Stubborn residue: use plain white vinegar briefly, scrub, and rinse immediately [5].
• General rule: start with the mildest method; escalate only if residue persists [2].
• Wet wipes are also acceptable for general residue removal [1].

Prohibited

• Steel wool, wire wheels, abrasive pads, or power tools.
• Caustic degreasers, oven cleaners, or strong acid/alkali cleaners [2].
• Strong alkalines such as ammonia or lye [3][4].
• Long solvent soaks; flammable solvent use near ignition sources [4].

Tools and Materials

• Wet wipes (optional) for convenience (e.g. quick clean on-site) [1].
• Plastic tub (large enough for full casing; chemical-compatible)
  • Our kit: clear polypropylene/PE tote ~26.5″×16″×6.6″, fits full casing and allows visual inspection.
• Nylon-bristled brush (bottle brush or toilet brush; non-metal)
  • Our kit: nylon bottle brushes and toilet brush.
• Non-metal scraper (silicone/nylon/plastic)
  • Our kit: silicone turner, rigid wide edge, non-scratching.
• Lint-free microfiber cloths
  • Our kit: ultra-soft auto-detailing cloths.
• Cotton swabs or small balsa sticks for O-ring grooves [1].
  • Our kit: craft sticks and cotton swabs
• Nitrile gloves
  • Our kit: team PPE supply.
• Mild dish detergent
  • Our kit: Dawn Original or unscented.
• Isopropyl alcohol (91–99%) for final wipe [3]
  • Our kit: 97% IPA.
• Plain white vinegar
  • Our kit: food-grade vinegar.
• Light machine oil or silicone O-ring lubricant (for threads only)
  • Our kit: 3-in-1 machine oil.
• Compressed air (optional)
  • Our kit: shop compressed air.

Procedure

1) Pre-Clean and Disassembly

1. Ensure hardware is cool. Remove from airframe per CTI instructions and airframe integration protocol [1].
2. Remove retaining rings, closures, nozzle, O-rings, insulators, and liner. Discard consumables [1].
3. Use scraper to dislodge loose residue without scratching anodized surfaces.

2) Detergent Wash

1. Fill tub with warm water and mild detergent.
2. Scrub bore, closures, threads, and O-ring grooves with nylon brush.
3. For stubborn residue, apply vinegar, scrub, and rinse immediately [5].
4. If needed, soak a paper towel in vinegar, press against the deposit for 15–30 minutes, then scrub. Repeat up to three times before re-washing in warm soapy water.
5. For O-ring grooves, use cotton swabs or small balsa sticks for precision cleaning [1].

3) Rinse and Dry

1. Rinse thoroughly with warm water until no suds remain [2].
2. Wipe dry with microfiber cloths or wet wipes; use compressed air to clear grooves and threads.
3. Optionally wipe with IPA to remove oils; allow to evaporate [3].

4) Inspection

• Check threads, grooves, and sealing faces for cracks, dents, or anodizing wear.
• Confirm O-ring grooves are clean and residue-free [1].

5) Lubrication and Storage

1. Apply a very light coat of oil or O-ring lubricant to threads only.
2. Reassemble loosely (finger-tight) for storage.
3. Store in a dry environment; keep elastomers away from solvents and sunlight.
4. CTI notes that a light coat of grease on the liner exterior can also aid future disassembly and cleanup [1].

Turnaround Timing

Clean as soon as possible after flight to prevent hardening of residue and corrosion [1].

Waste and Residue Handling

• Dispose of inert liners, nozzles, and wipes in household waste if fully cool, per local regulations [1].
• Do not pour vinegar or solvent waste into soil or drains; follow municipal hazardous waste guidance.
• For unburned propellant or smoke charges, follow CTI’s disposal instructions; this SOP does not cover energetic material disposal [1].

Notes & Rationale

• Tub size ensures full immersion and visibility.
• Nylon/PP brush and scraper remove residue without damaging anodizing.
• Dawn Original is effective, safe, and leaves little residue.
• IPA is fast-evaporating and safe for anodized aluminum [3].
• Extra tools like wet wipes, cotton swabs, and balsa sticks provide efficient groove cleaning [1].

References

[1] CTI Pro98 Instructions — Cleanup and maintenance guidelines
https://pro38.com/wp-content/uploads/2024/11/Pro98_Instructions.pdf

[2] Linetec — Cleaning Anodized Aluminum: Soap and water guidance
https://linetec.com/anodize/anodize-cleaning-maintenance/

[3] SAF (Southern Aluminum Finishing) — Cleaning and Maintenance of Anodized Aluminum
https://www.saf.com/faqs/how-do-i-clean-anodized-aluminum/

[4] Anodize Inc. — Care and Maintenance of Anodized Aluminum
https://anodizeinc.com/2020/05/care-and-cleaning-of-anodizing/

[5] Rocketry Forum — Community practice on vinegar for stubborn residue
https://www.rocketryforum.com/threads/cleaning-casings.114571/